Whenever discussing a new topic or subject, it is always essential to establish a common language or a group of proper definitions to discuss the topic adequately. The following text goes over some of the more common terms one might encounter when dealing with different measurement systems.
Definition:
Any measurement system that one might use may be broken done into three main elements. The elements of a generalized measurement system are
The sensing element of a generalized measurement system is the part of the system in direct contact with the measurement system's measurand.
The signal modification element of a generalized measurement system is the part of the system that takes the signal from the sensing element and modifies it (typically, it magnifies it). This adjusted signal is used by an individual to utilize the signal in a useful way.
The indicator of a generalized measurement system is the part of the system that allows the individual to use the measurement system to read the measurand's particular value.
The different elements of the generalized measurement system pertain to both analog and digital devices. Consider a glass thermometer. A glass thermometer is constructed of a glass tube with a large bulb on one end. The tube is evacuated, and in its place, a fluid is introduced inside the glass body. Mercury is a common fluid used, but it is often avoided nowadays due to the risk of mercury poisoning. Ethanol is a common alternative to mercury. Once the fluid has been introduced inside the glass body, the opening is sealed. When the thermometer experiences a temperature change, the thermometer's fluid rises and lowers the thermometer's body or stem. The fluid rises and falls due to changes in its density. With the understanding of how a glass thermometer works, the generalized measurement system components may be identified. Shown below in Figure 1 are the three parts of a generalized measurement system of a glass thermometer.